The present invention is directed to an electric motor assembly and more particularly to a motor assembly which includes a lead guard removably mounted inside a motor housing. The lead guard defines a space within the motor housing for connecting various motor control leads (both those coming into and those resident within the motor) and for protecting them from coming in contact with other motor components, particularly those that are moving.
Electric motors often have one or more components mounted therein that regulate the operation of the motor. Terminals of these components, as well as the terminals of the windings of the motor, must be interconnected and joined to external conductors (e.g., a suitable power source) so that the motor may operate. This is typically accomplished via an arrangement that allows conductors extending from these various terminals to be connected together at one location. This location may be defined by structures which are internal to or external to the motor housing (e.g., a "terminal box").
Lead guards include those that are mounted on the interior of the motor housing so as to protect motor conductors from dirt, moisture and moving motor components. These guards are welded onto an interior surface of the housing before the stator winding is installed because of room needed to weld and because of potential damage to the stator windings during welding. At least two problems exist with this arrangement. First, on certain sized stator windings, the lead guard must be bent out of the way when inserting the stator windings and bent back before any electrical leads can be routed. Bending causes "metal fatigue" to points at which the lead guard is bent as well as "structural fatigue" at the welding points. Second, because the lead guard is welded in the housing, when either part is damaged, both parts must be replaced. This adds cost both in terms of additional material and labor.
A lead guard mounted in the interior of the motor housing without welding, subsequent to the insertion of the stator windings, that protects conductors from dirt, moisture, and moving motor components would be a welcome improvement. It is an object of the present invention to provide such an improved lead guard and less costly assembly.
According to the present invention, an electric motor assembly comprises a motor housing, a stator mounted within the motor housing, a pair of end shields mounted adjacent opposing ends of the motor housing having bearings disposed therein for rotatably supporting a rotor adjacent the stator, and a removable lead guard mounted within the motor housing. The lead guard is mounted adjacent a conductor receiving opening in the housing. The lead guard defines a space within the motor housing wherein external and internal electrical conductors may be connected to each other and shielded from the rotating components of the motor assembly. In one embodiment of the invention, the lead guard is molded in a single piece from a thermoplastic material. The plastic lead guard comprises a generally flat portion and an upstanding portion that forms an angle to the perimeter of the flat portion to at least partially define the space within the housing. At least one slot is formed in the generally flat portion through which a conductor may be routed into the space defined by the lead guard. The lead guard has a stiffener integrally formed on a surface of the flat portion to provide strength reinforcement thereto.
In one embodiment of the present invention, the lead guard further comprises structure for guiding conductors entering the motor housing through the opening formed therein into the space at least partially defined by the lead guard to prevent the conductors from entering portions of the housing in which the stator and rotor are mounted. The guide structure is an integrally molded portion of the lead guard having a U-shaped cross section. This embodiment of the lead guard further comprises integrally molded structure for mounting the lead guard to the housing of the motor. The integrally molded mounting structure includes a plurality of flanges formed on opposing portions of the lead guard that engage corresponding slots formed in an edge of the motor housing. Shoulders and lips may be formed on the lead guard to engage respective inner and outer surfaces of the motor housing to anchor the lead guard in the housing. Integrally molded gussets may be provided between the mounting structure and a surface of the flat portion of the lead guard to strengthen the point of connection of the lead guard to the motor housing.
At least one slot may be formed in the upstanding portion through which a conductor may be routed. In one embodiment, this at least one slot may be U-shaped. One or more lead retaining structures in one-to-one correspondence to the number of slots in the upstanding portion may also be provided. These lead retaining structures extend opposite to and on both sides of the slot such that a space is formed between the one or more lead retaining structures and the at least one slot. The one or more lead retaining structures are intended to capture conductors that inadvertently move up in the at least one slot to prevent the conductors from being unintendedly removed therefrom. In one embodiment, the one or more lead retaining structures are integrally molded with the lead guard. A notch may be formed in each of the one or more lead retaining structures to aid in capture of conductors. As with the at least one slot, the notch may be U-shaped.
Other features of the lead guard may include: clamp bolt bosses formed at each of the opposing ends of the body, having holes formed therein which extend through the bosses to accept the body of a through-bolt; at least one or more holes formed through the generally flat portion to allow one or more conductors in the space of the lead guard to be secured via straps extending through the holes; and formation of the lead guard as a single structure from molded plastic material so that all surfaces thereof can be seen from at least one set of two-dimensional perspectives, the set including two different two-dimensional views of the lead guard.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.